A sample of deep Keck spectra for galaxies at 1 < z < 2.5 Sirio Belli (MPE), December 2018 sirio@mpe.mpg.de ################################# If you use these data in your publication, please cite Belli et al. 2014, ApJ, 783, 117 (for the LRIS spectra) and Belli et al. 2017, ApJ, 834, 18 (for the MOSFIRE spectra). ################################# This directory contains 167 Keck spectra of high-redshift galaxies. The primary targets are massive quiescent galaxies, but low-mass and/or star-forming objects are also present. The sample was obtained with the main goal of studying the rest-frame optical stellar continuum; the main features that were targeted are the Balmer absorption lines, CaII H and K, 4000A break, G band, and also the [OII] emission line. However, the exact rest-frame wavelength range is different for each object, depending on resdshift and position on the slitmask. Each of the 167 spectra yielded a spectroscopic redshift measurement via absorption and/or emission lines; more galaxies were targeted during the observations but no identifiable features could be detected in their spectra. The spectra were obtained during two distinct campaigns: 1) LRIS sample: 103 spectra of galaxies at 1 < z < 1.6 obtained with Keck LRIS, from these two studies: - Newman et al. 2010, ApJ, 717, 103 - Belli et al. 2014, ApJ, 783, 117 The spectra are also used in this study: - Belli et al. 2015, ApJ, 799, 206 Note that one spectrum (ID 17070) was actually obtained using Keck/DEIMOS. 2) MOSFIRE sample: 64 spectra of galaxies at 1.5 < z < 2.5 obtained with Keck MOSFIRE, from these two studies: - Belli et al. 2014, ApJL, 788, 29 - Belli et al. 2017, ApJ, 834, 18 The spectra are also used in this study: - Belli et al. 2019, ApJ, 874, 17 Physical properties measured from these spectra, such as stellar velocity dispersion and stellar ages, can be found in the above publications. However, each publication uses slightly different criteria to select the subset of spectra to use in the scientific analysis. Typically, about half of the observed spectra were discarded in the analysis because of low signal-to-noise ratio, or because the galaxies are not quiescent. ################################# The file Keck_sample.xlsx contains two spreadsheets: The first spreadsheet lists the basic properties for each galaxy in the sample: - Instrument: the Keck instrument used for the spectroscopic observations - ID_Belli: the ID used in the papers mentioned above - ID_3DHST: the ID used in the 3D-HST catalog. Five objects do not belong to the 3D-HST catalog; in these cases their ID_3DHST is a negative number. - Field_3DHST: one of the five fields of the CANDELS and 3DHST survey (EGS, COSMOS, GOODS-S, GOODS-N, UDS). This is required, in addition to ID_3DHST, for the unique identification of an object in the 3DHST catalog. The five objects not in the 3DHST catalog have an empty Field_3DHST; they are either in the SSA22 field, which was not observed by CANDELS, or lie just outside the CANDELS footprint. - RA: J2000 right ascension - DEC: J2000 declination - maskname: name of the slitmask used for the spectroscopic observations - redshift: spectroscopic redshift measured from the Keck data The second spreadsheet lists all the slitmasks used for the observations. For each slitmask, the exact frames that were used in the data reduction and the corresponding exposure time are given. This makes it possible to trace each reduced spectrum back to the raw frames in the Keck archive. Note that to uniquely identify the observations both the slitmask name and the instrument name are needed: for example, the LRIS COSMOS2 mask is a completely different mask from the MOSFIRE COSMOS2 mask, and has different targets. ################################# Each spectrum is stored as a structure in a FITS file, and can be open, for example, with the IDL command: IDL> spec = mrdfits('lris_27877.fits', 1) The structure includes some of the fields described above: ID_Belli, ID_3DHST, Field_3DHST, RA, DEC. Additional fields are: - LAMBDA: array with the observed wavelength, in angstrom - FLUX: array with the observed flux, in units proportional to Flambda ( erg/(s cm^2 A) ). - IVAR: array with the inverse variance spectrum; 1/sqrt(IVAR) is the uncertainty on the flux - SKY: array with the observed sky flux, in arbitrary units NB: The fluxes are telluric-corrected, which means that the small-scale absorption features introduced by the atmosphere have been removed. The MOSFIRE spectra have also been flux calibrated using standard stars, and for these objects the FLUX array is in units of 10^(-18) erg/(s cm^2 A). However, the absolute flux calibration is strongly affected by slit loss, and for an accurate measurement it is best to compare the observed flux of a galaxy to broadband photometric measurements. The LRIS spectra have not been flux calibrated: the units are arbitrary, and the spectral shape is strongly affected by the instrumental response.